Vacuum pump unit



Oct. 15, 1963 Original Filed May 26, 1959 A. LORENZ VACUUM PUMP UNIT 5 Sheets-Sheet 1 FIG. 2

FIG.

A. LORENZ VACUUM PUMP UNIT Oct. 15, 1963 5 Sheets-Sheet 2 Original Filed May 26, 1959 Oct. 15, 1963 A. LORENZ 3,107,047

VACUUM PUMP UNIT 5 Sheets-Sheet 3 I Original Filed May 26, 1959 Oct. 15, 1963 v A. LORENZ 3,107,047

' VACUUM PUMP UNIT Original Filed May 26, 1959 5 Sheets-Sheet 4 FIG. 5A

FIG. 5B

Oct. 15, 1963 A. LORENZ 3,107,047

VACUUM PUMP UNIT Original Filed May 26, 1959 5 Sheets-Sheet 5 United States Patent 3,107,947 VACUUM PUMP UNIT Alpert Lorenz, Hanan am Main, Germany, assignor to W. C. Heraeus G.m.h.H., Hanan am Main, Germany, a corporation of Germany Continuation of application Ser. No. 815,9il6, May 26, 1959. This application Mar. '7, 1952, Ser. No. 17?,286 19 Claims. (Cl. 230-1525) The present invention relates to improvements in vacuum pumps of the rotary piston type as generally described, for example, in the United States patent to Kinney, No. 1,061,181.

This application is a continuation of my copending application No. 815,906 filed May 26, 1959, now abandoned.

Such rotary piston pumps with one or several evacuating stages have at least one cylindrical piston chamber with a substantially cylindrical piston revolving therein eccentrically along the inner .wall of the piston chamber. This piston has a straight hollow slide member integrally secured thereto which is slidable within a guide member and serves as a suction inlet channel connecting the inlet climber of the pump with the vacuum side of the piston chamber. The manufacture of these pumps is rather complicated and expensive and requires special machine tools, especially because of the difiiculties involved in producing the cylindrical piston with the straight extension thereon forming the slide member projecting from the periphery of the piston toward one side.

In order to simplify the manufacture of such pumps, they have so far been generally designed so that the diameter and the length of the cylindrical part of the piston were maintained within a constant ratio to each other, usually within a ratio of 1:1. Consequently, if the difierent pumps were built for a different suction output, they also varied in height and their inlets and outlets were disposed at different levels. The construction of the entire vacuum system therefore had to be made in accordance with the particular size of the pump used and if, for example, it became necessary to apply a bigger pump than the pump for which the vacuum system was originally built, it was not possible simply to exchange the pumps but it required an expensive and time-consuming reconstruction of the vacuum system to connect such bigger pumps thereto.

Furthermore, if a pump of a difterent size became necessary, or if certain components of the installed pump became defective after a prolonged use, the entire pump had to be exchanged. The pumps were of such a design that an exchange of individual components was impossible at least at the place of its use, and it could not be carried out by the purchaser of the pump even though he had a well equipped workshop and expert mechanics, and it was at least necessary to return the pump to the manufacturer for rebuilding or repairing the same. The components of one pump size could also never be used for a pump of any other size, and even though a plurality of pumps of different sizes was available, the components of these different pumps could never be used to assemble a single new pump regardless of how urgently it might be needed.

It is an object of the present invention to provide a new pump design which eliminates all of the abovennentioned disadvantages and permits the assembly of pumps of dilferent output sizes by means of the same components or at least by a series of similar components which may be manufactured by means of the same tools and according to similar standards.

Another object of the present invention consists in providing a new pump design in which the circumference "ice of the housing of a pump of one output size is identical in a radial direction with the circumference of the housing of any other output size, or, in other Words, in which the pumps of various output sizes are of the same height, and in which the pump inlets and outlets and especially the former, are therefore located at a peripheral point of the pump housing at the same level or height from the base of the pump, so that any one of a large variety of pumps of difierent output sizes may be connected to the same vacuum system without requiring any changes in the latter.

A further object of the present invention is to provide a pump design of such a simple construction as to permit the purchaser of a pump or his own mechanics to assemble and disassemble the same without any great diniculty, and not only to exchange the components of the pumps of one output size for one another but also to use these same components for assembling a pump of a larger or smaller output size and to build a new pump from the components of several old pumps of the same size or different sizes.

The present invention is therefore of the greatest advantages both to the manufacturer for attaining an economical production of pumps of different output sizes, especially in a mass production thereof, and also to the purchaser or user of the pumps as it enables him to repair them himself or to exchange their components without difficulty, and, with a certain stock of pumps of different output sizes, to assemble pumps of still other sizes. Thus, the user of the pumps may easily assemble a pump from an available supply of pump components of different sizes in accordance with the particular output desired or required for the respective evacuation job and without requiring any change in the arrangement and position of the existing 'vacuum system and its connecting flanges to the vacuum pump.

The present invention further resides in a plurality of features and the combination thereof with each other. These features consist of:

(a) The partitions separating at least the individual rotary pistons and pump chambers of a multiple-stage pump from each other, and preferably also the partitions separating the individual guide elements of the slide members on the pistons as well as the inlet or, suction chambers of each stage from each other are removable from the pump housing.

(b) Regardless of the output size of the difierent pumps their rotary pistons and pump chambers all have the same cross sectional size.

(c) The length of any piston and any pump chamber of a pump with several pistons or with difiierent outputs forms the term of an exponential series and preferably an integral multiple of a certain basic term or unit, which itself may or may not be applied in any of the pumps and may form only a fraction of the longitudinal dimension of the pump as actually applied. Thus, in the simplest case, the length of the diiferent pistons might be any measurement in accordance with the terms 1, 2,

4, 8, 16, 32, etc.

(d) Each individual pump has a horizontal drive shaft and is composed of certain uniform parts applying to all pump sizes, that is, of a housing with an exchangeable motor mounted in the same position on all housings, of a wall or partition closing ed the speed reduction gear, of a pump element forming one of a series each of which is adapted to produce a different output, and of an outer end wall which in a very smadl pump, that is in one with one or more thin or narrow pistons, may also form the base of the pump since the pump is then turned over so that its drive shaft extends perpendicularly rather than horizontally as the height of the pump housing would otherwise exceed the width thereof to suchan extent that the pump could no longer be mounted with sufficient stability.

(e) The longer pistons of a pump with several pistons of different length are, vfor well known reasons of statics and dynamics, always disposed more closely to the driving elements, that is, to the speed reduction gear, and the latter is also provided with a counterbalance to compensate any unbalance in the revolving system.

(1) Two or more pumps of a difierent output may be combined so as to form one double-pump unit, which has a single drive shaft for both pump pistons, by applying the same kind of apartition to all output sizes for separating the individual pumps.

Obviously, there are some pump components which cannot be built for all output sizes of the same dimensions in any but the longitudinal directions and which mustbe built specially for the respective output size of a pump or at least for a certain range of output sizes. Thus, for example, the motor as well as the oil-dust separator have to be different for at least some of the greatly different output sizes of a large series of pumps, although they may also be exchangeable for those of other sizes by suitable connecting means.

These and other'additional objects, features, and ad vantages of the present invention will become further apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings, in which- FIGURE I shows a cross section of a pump according to the invention, taken along line II of FIGURE 2;

, FIGURE 2 shows a cross section of the pump taken along line II-II of FIGURE 1;

FIGURE 3 shows a cross section of the pump taken along line III-III of FIGURE 2;

FIGURE 4 shows a cross section of a pump similar to that of FIGURE 2 but provided with three pistons;

FIGURES 5A, 5B, 5C illustrate the interchangeability of the rotary pistons between pumps of different output s1zes;

FIGURES 6A, 6B, 6C, 6D, 6E, 6F, 66, 6H, 61, 6!, 6K are diagrammatic illustrations of a series of pumps according to the invention;

FIGURE 7 shows a front view of a pump with narrow pump pistons and pump chambers; while 7 FIGURE 8 shows a front view of a pump unit consisting of two pumps of widely difierent output sizes.

Referring to the drawings, the vacuum pump according to the invention as illustrated in FIGURES 1 and 2 is a two-stage pump of a type known as such in which two individual pumps are connected in series within a common housing 1, the pump at the left side of FIG- URE 2 forming the first or high-vacuum stage and the pump at the right side forming the second or pre-vacuum stage in which the gases evacuated by the first stage are compressed at least to atmospheric pressure to be expelled toward the outside. Each pump housing 1 contains a cylindrical pump chamber 2 and 2' of the same diameter. These pump chambers are closed toward the outside by end walls 3 and 3' and are separated from each other by a circular partition 4 having a diameter equal to the diameter of the chamber 2. Both pumps or pump stages are operated by a common drive shaft 5 which carries a pair of eccentrics 6 and 6 which are rotatable within a pair of cylindrical pistons 7 and 7' of an equal diameter. These pistons are thus rotated eccentrically within pump chambers 2 and 2' and along the inner walls thereof. Each piston 7 and 7 has an extension 8 and 8', respectively, projecting outwardly from a peripheral point thereof and forming a slide member which is slidable in its longitudinal direction within a guide member 9 or 9 which is rotatable within a cylindrical chamber 10 or 10 and adapted to oscillate therein in accordance with the eccentric movement of the piston 7 or 7.

The two chambers 10 and 10 formed fromv a second chamber which extends between the end walls of the housing 1 are also in a straight alignment with each other and parallel to pump chambers 2 and 2'. They merge above into inlet chambers 11 and 11, which are formed from a third chamber extending between the end walls of the housing 1. These second and third chambers are parallel to each other and to the cylindrical chamber from which the pump chamber 2 and 2' are formed. The inlet chambers 11 and 11' communicate with the suction side of pump chamber 2 or 2', respectively, through an inlet channel 12 or 12 extending through slide member 8 or 8' and terminating at its lower end into the. respective pump chamber through apertures 13 which may be, for example, of a triangular shape.

from chambers 10 and 11 of the second or pre-vacuum pump stage by a partition 14 which has a shape equal to the transverse shape of the chambers 10 and 11. Pump chamber 2' of the first stage of the pump is connected at the vacuum side thereof by one or more outlet channels to an oil chamber which contains a certain supply of oil and is disposed above pump chamber 2'. This outlet channel and oil chamber are not visible in FIGURE 2 as they are located'in pump housing 1 behind chambers 10' and 11'. The mentioned oil chamber of the first pump stage is connected by a channel with the inlet chamber 11 of the second pump stage, as shown in FIG- URE 1, and through the latter and inlet channel 12 in slide member 8 with pump chamber 2. The air or gases entering through the main inlet 15 and conveyed by piston 2' through the outlet channel of the first pump chamber pass through the oil in the mentioned oil chamber of the first pump stage and then through the connecting channel, not shown, into inlet chamber 11 of the second pump stage and then through channel 12 into pump chamber 2 where they are compressed by piston 7 and forced through an outlet channel 16 past an outlet valve 17 into and through oil chamber 18 and then through an oil-dust separator 19 of any suitable design above housing 1 and through the outlet 29 either directly toward the outside or into a pipeline connected to outlet 20. The oil vapor or oil dust produced by the passage of the ejected gases through the oil contained in oil chamber 18 is partly condensed within chamber 18 and more completely separated from the gases within separator 19.

As illustrated in FIGURE 2, the two pump pistons 7 and 7' are turned relative to each other at an angle of Pump chamber 2' and piston 7' of the high-vacuum stage at the left side of FIGURE 2 are of a greater length than pump chamber 2 and piston 7 of the prevacuum stage at the right side of FIGURE 2. Accordingto the invention, pump chambers 2 and 2' areoriginally continuous and are machined in one continuous process as one large bore in housing 1. Partition 4 be tween the two chambers 2 and 2' may be inserted into this bore from either end and removably securedin the proper position by suitable means, not shown,'and sealed relative to housing 1 by a suitable gasket 21. Partition 14 may either be integral with housing 1 or as shown in FIGURE 2, it may also be removably secured by suitable means between chambers 10, 11 and 10, 11 and sealed relative to housing 1 and partition 4 by a gasket 22. If partition 14 is likewise removable, chambers 10, 11 and 10', 11 are continuous and may also be produced in housing 1 by one operation. Partition 14 may then also be inserted into housing 1 from either end. The removability of partitions 4 and 14 or at least of partition 4 has the great advantage that the two pistons do not have to be inserted from the opposite ends of the housing but may be inserted successively from either end so that more than two pistons may be mounted adjacent to each other within one pump chamber. End walls 3 and 3 are likewise removably secured to housing 1 by Chambers 10' and 11' of the first or high-vacuum pump stage are separated a bolts 23 and likewise hermetically closed by suitable gaskets, not shown. Gaskets 21 and 22 may be replaced or supplemented by any well-known sealing means or sealing devices and are merely indicated as an illustration of such means.

This is illustrated in FIGURE 4 which shows a twostage vacuum pump with three rotary pistons. Whereas pump chamber 2' of the high-vacuum stage in FIGURE 2 has a length approximately twice as great as pump chamber 2 of the pre-vacuum stage, the entire pump chamber 25 of the high-vacuum stage of FiGURE 4 has a length approximately four times as great as pump chamber 2. This pump chamber 25 is divided'by a removable partition 25 similar to partition 4 into two equal chambers 2 and 2", each of which is thus approximately twice as long as pump chamber 2. Each pump chamber 2' and 2" ccording to FIGURE 4 contains a rotary piston 7 and '7", respectively, with its associated eccentric 6 and 6" on shaft 5, slide member 8 and 8", and guide member 9' and 9", respectively. Both pump chambers 2' and 2 communicate with a single inlet chamber 27 which is provided with a main inlet 15. In this embodiment a removable partition 23 separat s the chambers containing the guide members 9 and 9" but it does not extend through inlet chamber 27. Piston 7 and 7' are again diametrically opposed to each other on shaft 5, while piston 7 is diametrically opposed to piston 7". Pump chamber 2, 2' and 2" are again originally continuous and produced in one operation. This likewise applies to the chamber which by the subsequent insertion of partitions 14 and 28 is divided into inlet chambers 27 and El, and the separate chambers containing guide members 9, 9, and 9", respectively.

Since all of the pistons of this and any other pumps according to the invention are of the same diameter and the pump chambers also all have the same diameter, the output of each piston depends only upon its length and the length of the respective pump chamber. Since in the embodiment according to FIGURE 4 the length of the total pump chamber 25 and of the two pistons 7 and '7 of the high-vacuum stage has been doubled as against pump chamber 2 and piston 7' in FIGURE 2, the suction volume and output of this pump stage is also doubled.

By increasing the output of each pump and pump stage solely by increasing the length of the pump chamber and pump piston, a number of very important advantages are attained. The outer height of the pumps will always be the same and thus also the height h (FIGURE 4) of the outlet 15 from the ground or supporting structure. Therefore, if the original pump on a particular vacuum system should for any reason be exchanged for one with a larger or smaller output, this can be easily done without any changes on the vacuum system and simply by connec ing the new pump'to the connecting flange of the vacuum system. Furthermore, the pistons '7, eccentrics 6, and guide members 9 of different pumps may be easily exchanged for one another, provided they are of the same lengths. The similarity of these dimensions of the pumps also considerably facilitates the production of any one pump as well as of a large series of pumps each of which has a diiierent output, and it therefore also considerably reduces the cost of manufacture of.

any pump of the series.

As previously stated, the longer pistons of the highvacuutn stage at the left side of the two-stage pumps according to FEGURES 2 and 4 are twice as long as the piston of the pre-vacuum stage at the right side. Therefore, the two stages of the pump according to FIGURE 2 have an output volume of 2:1, while those according to FIGURE 4 have an output volume of 4:1. It the individual pumps are not connected in series but each operates as a one-stage pump, all or" the pistons may crate in parallel. The volumetric ratio of 2:1 between the two stages of one pump has proved in actual practice in most cases to be the most successful.

If, according to a funther important feature of the invention, the pistons of the difierent pumps of one series are made of a length, each of which corresponds to a certain multiple of a certain basic term of an exponential series, the pistons which correspond to any one term within the series but belong to diifenent pump sizes may be easily exchanged for each other. term itself may in that case not be applied in any pump, but the smallest pump of the series may already have a piston length which corresponds to a multiple of such basic term. In compliance with the volumetric ratio of 2:1 between the two stages of each pump, as above described, it has been found most advisable also to make the gradation between the individual pump sizes in accordance with this ratio. If each of the pumps of the entire series has two pistons as in FIGURE 2, the following gradations may be attained:

Pump Output Piston length in multiples of in any arbibasic term trary units of revolution Stage I Stage II 2 2 1 4 4 2 8 8 4 16 16 8 etc. etc. etc.

The above table indicates that with such a gradation two pistons of consecutive pump sizes may always be exchanged for one another. This has been illustrated in FIGURES 5A, 5B, 5C which are self-explanatory. It also indicates that vn'th an available stock of smaller pistons, it is possible to compose one or more longer pistons or even the two pistons of a pump with a volumetric ratio of 4:1. Obviously, instead of making the pistons in accordance with the exponential series 1, 2, 4, 8, etc., it is also possible to make them according to any other exponential series, "for example, 1, 3, 9, 27, etc.

An important object of the invention consists in designing the pumps so that the larger piston of one pump size of a series of pumps may serve as the smaller piston of the next larger pump size or, vice versa, that the smaller piston of one pump size may be inserted into the next smaller pump to serve as the larger piston therein. Due to such an interchangeability it is possible in the case of a mechanical breakdown to interchange the pistons of difierent pumps and even of different-sized pumps so as to effect a quick repair of at least one pump. Since, as previously mentioned, the pump connections of both pump sizes are identical, it is also possible to exchange one entire pump for the other. Thus, by one substitution or another, it is always possible with a certain number of pumps of the same size or different sizes to maintain an ex sting vacuum system in operation with only a very short interruption for making the exchange of pumps or pump pistons.

The pump according to FIGURE 4 differs from that according to FIGURE 2 also by illustrating the drive mechanism thereof. It consists of a gear housing 29 containing a speed-reduction gear which consists of a larger gear Wheel 30' on the drive shaft 5 of the pump and a smaller gear wheel 3%" on the drive shaft 31 of the electric motor 32.

As previously mentioned, the eccentrics 6, 6', and 6" of pistons '7, 7, and 7" which are slidable thereon are staggered at an angle of relative to each other. The masses of eccentric o and piston '7 then completely balance the masses of the right half of eccentric 6' and piston 7' both statically as well as dynamically. The same applies to the masses of the left half of eccentric 6 and piston 7 which completely balance the masses of the right half of the masses of the adjacent eccentric 6" The basic -a disk which is considerably thinner or narrower than the length of the left half of eccentric 6" and piston 7". Such a balancing of the uneven and unsymmetn'cally arranged rotary pistons of vacuum pumps also constitutes a new feature of the invention and has the result that such a pump does not have to be rigidly secured to a foundation or supporting stnucture but may even be mounted on rollers 34 so as to be easily movable from one place to'another. The individual pump unit may therefore be alternately connected to different apparatus which obviously means that it can be used to the :fullest extent, rendering its operation very economical. The pump according to the invention operates so quietly that, despite its easy movability, it will remain perfectly stationary at the selected position and will not transmit any vibrations to the vacuum apparatus which is connected thereto. If only a small vessel is to be evacuated, it may be connected to and supported by the suction inlet 15 of the pump and be moved with the latter from one place to another. This is important if the evacuation of such a vessel should not be interrupted even during transport. This as well as numerous other advantages are possible only through the complete balancing of the pump system, both dynamically and statically.

, Thepump design as illustrated in FIGURE 6, either with two or three pistons, has the further advantage that it permits an assembly of new pumps of any desired output size from a series of components kept in stock. The components necessary for this purpose are diagrammatically illustrated in FIGURES 6A through 6K. The driving parts 29 and 32 and the end walls 3 and 3' may be connected to any one of a large series of pump housings 35 to 42 having a piston length 1 as indicated in FIGURE 6 underneath each pump. For interchanging the difierent pumps 35 to 42, there are only a few parts which have to be exchanged, such as the flanged-on motor 32 which has to be selected in accordance with the required driving power, the counterbalance 33 (shown in FIGURE 4 but not in FIGURES 6A through 6K) on gear wheel 30', the oil-dust separator 19 as shown in FIGURES 1 and 2 on the outlet of the pump, and the pump base 45. In the event that the length of the pump, for example, pumps 4% to 42, is so small that it is advisable to turn the entire pump unit over upon its end wall, as shown in FIGURE 7, this end wall 43 then forms the base of the pump, so that the motor and pump shafts will be disposed perpendicularly. These parts are easily exchangeable and they are also of minor importance in the production of the pumps and require less effort.

than the other parts.

The pump series illustrated in FIGURES 6A through 6K by no means includes all the possibilities of combination and may be extended considerably. Thus, for example, it does not include any pumps with three pistons, as shown in FIGURE 4; and anyone of the larger pumps of the series may also be easily converted in the manner as previously described to accommodate three pistons.

A pump series similar to that shown in FIGURE 6A through 6K or designed according to a different exponential series has the advantage that'standard components may be assemblied to form pumps of a different output, all of which are equally constructed and have the same height, and can therefore be easily connected to the same vacuum apparatus without requiring the same to be changed. Furthermore, their rotary pistons and eccentrics may be easily exchanged and each of them may at least be used in a pump of the next larger or smaller size or two or more smaller pistons and eccentrics may be combined tov form one longer piston by simply attaching themto each other.

FIGURE 6K also diagrammatically illustrates a partition 44 which may be applied if two separate pumps of a difierent output but driven by the same shaft are to be connected to each other, as shown, for example, in FIG- URE 8. This illustrates the very important application of such pumps in which a pump 35 having a large output, [for example, of 32 units, is coupled with a pump 39 of a much smaller output, for example, of 2 units. Such a pump combination is especially desirable if, for example,

a large vacuum vessel is to be evacuated and if it is necessary at the same time to evacuate the sealing chambers between flange connections of the vacuum system which requires only a small suction output and has to be applied only simultaneously with the evacuation of the large vessel. The output of such coupled pumps for the mentioned purpose is preferably made within a ratio larger than 5:1. Since both pumps are driven by the same pump shaft and the same motor 3-2, they will always be operated or switched off simultaneously. When connecting such a small pump to such a large pump, it is also possible to dispense entirely with a base for the small pump and to attach it merely to the large pump, as illustrated in FIGURE 8, so that the base 45 of the latter will also support the small pump. 7

The features of the new pump design as above described have made it possible for the first time to manufacture pumps of a unitary construction with an output ranging from 240 in. per hour to 3 111. per hour. This constitutes a ratio of to 1. Such a ratio could previously be attained only by adding a large number of indi- 'vidual pump units'to each other which involved an almost prohibitive expense, a complicated apparatus for combining the numerous pump units, and a great waste,

of energy for driving the pumps. According to the invention, however, such a large output ratio may be attained by a series of pump units with similar exchangeable elements which are larger or smaller in only one direction and may be produced with the same machines and tools and exchanged by any experienced mechanic without requiring a return ofthe pump to the manufacturer for any alterations or repairs.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, What I claim 15:

1. In a multistage vacuum pump of the rotary piston type having one pump housing with removable end walls, a cylindrical chamber of a uniform diameter within and extending between the end walls of said housing, said housing being formed with second and third chambers extending through said housing between the end walls thereof parallel and adjacent to each other and parallel to said cylindrical chamber with the second chamber merging into the cylindrical chamber peripherally thereof, at least one movable transverse partition within said housing and in said chamber and dividing said cylindrical chamber into at least two pump chambers, said second chamber into two guide chambers and said third chamber into two inlet chambers, respectively, said partition being in sealing engagement with the peripheral walls of said chambers, each of said guide chambers being disposed between one of said inlet and pump chambers, one of said pump chambers, inlet chambers and guide chambers together forming a first high-vacuum stage, the other pump chamber, inlet chamber and guide chamber together forming a second prevacuum stage, a main inlet in said housing connected to said inlet chamber of said first stage, and an outlet in said housing connected to said second stage, a drive shaft extending cenaroma? trally and longitudinally through said cylindrical chamber and rotatably mounted in said end walls and in a bore in said partition, at least two cylindrical eccentrics of equal diameter removably secured to said shaft and each disposed within one of said pump chambers and projecting from said shaft in diametrically opposite directions relative to each other, at least two cylindrical pistons of equal diameter, each of said pistons being rotatable slidable on each of said eccentrics, a straight slide member integrally secured to each of said pistons and projecting radially tfrorn the periphery thereof, at least two guide members, each of said guide members being rotatably mounted in each of said guide chambers and having an aperture extending diametrically therethrough, said slide member being slidably mounted within said aperture and having an inlet channel therein connecting said inlet chamber with the vacuum side of said pump chamber at one side of said piston, said housing further containing an oil chamber in each of said stages, valve means in said oil chambers, one of said oil chambers being interposed between and connected to said pump chamber of said first stage and said inlet chamber of the second stage, and the other oil chamber being connected to said pump chamber of said second stage and to said outlet.

2. A vacuum pump as defined in claim 1, in which said interconnected second and third chambers also have uniform dimensions throughout their length.

3. A vacuum pump as defined in claim 1, wherein said partition comprises two partition members, positioned in the same plane in end to end relationship each of said partition members being individually separable from each other and individually secured to and removable from said housing, one of said members separating said pump chambers from each other and the other member separating said inlet and guide chambers of each stage from each other.

4. A vacuum pump as defined in claim 1, further comprising means ;tor hermetically sealing said partition to said pump housing.

5. A vacuum pump as defined in claim 1, further comprising a gear housing removably secured to one of said end Walls and having interconnected speed reduction gear wheels therein, a motor remo-vably secured to said gear housing and having a shaft, one of said gear wheels being secured to said motor shaft and the other gear wheel being secured to said pump shaft.

6. A vacuum pump as defined in claim 1, further comprising an oil separator removably secured to said housing and connected to said outlet.

7. A vacuum pump as defined in claim 1, further comprising a second vacuum pump similar to said first pump and removably secured to one end of said first pump and driven by said shaft of said first pump, said first pump having a suction output at a ratio or at least to 1 to the suction output of said second pump.

8. A vacuum pump as defined in claim 1, wherein said housing, and said pump chambers and pistons With in said housing form pants of one multistage pump of a series of pumps in each of which each housing, pump chamber and piston has the same diameter as that of every other housing pump chamber and piston, respectively, but a length difierent from the length of the lionsing, pump chamber and piston of every other pump of said series.

9. A Vacuum pump as defined in claim 8, wherein said adjoining second and third chambers within each housing of said series of pumps have substantially the same dimensions transverse to the direction of said drive shaft.

10. A vacuum pump as defined in claim 8, wherein at least said housing, said pump chambers and said pistons of each pump of said series each has a length corresponding to a difierent term of an exponential series.

11. A vacuum pump as defined in claim 8, wherein at least said partition and said end walls of one pump of said series have substantially the same dimensions as the partition and end walls of any other pump of said series.

12. A vacuum pump as defined in claim 8, wherein said pistons within each pump of said series have a different length, the longer piston having a length equal to the length of the shorter piston oi the next larger pump of said series.

13. A vacuum pump as defined in claim 8, wherein said main inlet on said housing of one pump of said series is disposed at the upper side of said pump and at the same level as the outlet of any other pump of said series.

14. A vacuum pump as defined in claim 8, wherein said housing, said pump chambers, said pistons, said inlet and guide chambers, and said guide members of each pump of said series each has a length corresponding to a multiple of a basic term of an exponential series.

15. A vacuum pump as defined in claim 14, wherein said basic term of said exponential series forms only a fraction of the terms corresponding to the minimum lengths of said (housing, pump chambers, pistons, inlet and guide chambers, and guide members of any pump of said series.

16. A Vacuum pump as defined in claim 14, wherein said exponential series is graduated according to the terms 1, 2, 4, 8, 16, 32.

17. A vacuum pump as defined in claim 8, further comprising driving means, and means for removably securing said driving means to one of said end walls of said housing of one pump of said series in the same position as on the corresponding end Wall of any other pump of said series.

18. A vacuum pump as defined in claim 17, wherein said pistons Within each pump of said series have a different length, the longer piston being disposed within the pump chamber adjacent to said driving means, and means connected to said driving means for statically and dynamically counterbalancing the difierence in mass between said pistons so that said pump will operate substantially without vibrations.

19. A vacuum pump as defined in claim 17, further comprising an end wall adapted to be exchanged for the other end wall of said housing remote from said driving means and to be secured to said housing, said last end wall forming a base for supporting said pump in a position in which said pump shaft and said driving means are disposed perpendicularly.

References Cited in the file of this patent UNITED STATES PATENTS 1,271,729 Kmistufek July 9, 1918 1,677,780 Jaworowski July 17, 1928 2,181,168 Barnes Nov. 28, 1939 

1. IN A MULTISTAGE VACUUM PUMP OF THE ROTARY PISTON TYPE HAVING ONE PUMP HOUSING WITH REMOVABLE END WALLS, A CYLINDRICAL CHAMBER OF A UNIFORM DIAMETER WITHIN AND EXTENDING BETWEEN THE END WALLS OF SAID HOUSING, SAID HOUSING BEING FORMED WITH A SECOND AND THIRD CHAMBERS EXTENDING THROUGH SAID HOUSING BETWEEN THE END WALLS THEREOF PARALLEL AND ADJACENT TO EACH OTHER AND PARALLEL TO SAID CYLINDRICAL CHAMBER WITH THE SECOND CHAMBER MERGING INTO THE CYLINDRICAL CHAMBER PERIPHERALLY THEREOF, AT LEAST ONE MOVABLE TRANSVERSE PARTITION WITHIN SAID HOUSING AND IN SAID CHAMBER AND DIVIDING SAID CYLINDRICAL CHAMBER INTO AT LEAST TWO PUMP CHAMBERS, SAID SECOND CHAMBER INTO TWO GUIDE CHAMBERS AND SAID THIRD CHAMBER INTO TWO INLET CHAMBERS, RESPECTIVELY, SAID PARTITION BEING IN SEALING ENGAGEMENT WITH THE PERIPHERAL WALLS OF SAID CHAMBERS, EACH OF SAID GUIDE CHAMBERS BEING DISPOSED BETWEEN ONE OF SAID INLET AND PUMP CHAMBERS, ONE OF SAID PUMP CHAMBERS, INLET CHAMBERS AND GUIDE CHAMBERS TOGETHER FORMING A FIRST HIGH-VACUUM STAGE, THE OTHER PUMP CHAMBER, INLET CHAMBER AND GUIDE CHAMBER TOGETHER FORMING A SECOND PREVACUUM STAGE, A MAIN INLET IN SAID HOUSING CONNECTED TO SAID INLET CHAMBER OF SAID FIRST STAGE, AND AN OUTLET IN SAID HOUSING CONNECTED TO SAID SECOND STAGE, A DRIVE SHAFT EXTENDING CENTRALLY LONGITUDINALLY THROUGH SAID CYLINDRICAL CHAM- 